OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 24 — Nov. 21, 2011
  • pp: 24816–24821
« Show journal navigation

All-optical virtual private network and ONUs communication in optical OFDM-based PON system

Chongfu Zhang, Jian Huang, Chen Chen, and Kun Qiu  »View Author Affiliations


Optics Express, Vol. 19, Issue 24, pp. 24816-24821 (2011)
http://dx.doi.org/10.1364/OE.19.024816


View Full Text Article

Acrobat PDF (1633 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We propose and demonstrate a novel scheme, which enables all-optical virtual private network (VPN) and all-optical optical network units (ONUs) inter-communications in optical orthogonal frequency-division multiplexing-based passive optical network (OFDM-PON) system using the subcarrier bands allocation for the first time (to our knowledge). We consider the intra-VPN and inter-VPN communications which correspond to two different cases: VPN communication among ONUs in one group and in different groups. The proposed scheme can provide the enhanced security and a more flexible configuration for VPN users compared to the VPN in WDM-PON or TDM-PON systems. The all-optical VPN and inter-ONU communications at 10-Gbit/s with 16 quadrature amplitude modulation (16 QAM) for the proposed optical OFDM-PON system are demonstrated. These results verify that the proposed scheme is feasible.

© 2011 OSA

1. Introduction

Optical orthogonal frequency-division multiplexing-based passive optical network (OFDM-PON) is a subject of the great interest for recent research works in optical communications. Due to its high spectral efficiency, high dispersion tolerance and high flexibility on dynamic bandwidth allocation, optical OFDM-PON has been recognized as a promising candidate for the future optical access networks [1

1. N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Commun. Mag. 48(7), 70–77 (2010). [CrossRef]

]. The performance improvement in optical OFDM-PON [2

2. J. L. Wei, C. Sánchez, R. P. Giddings, E. Hugues-Salas, and J. M. Tang, “Significant improvements in optical power budgets of real-time optical OFDM PON systems,” Opt. Express 18(20), 20732–20745 (2010). [CrossRef] [PubMed]

], featuring multi-band OFDMA in WDM-OFDMA-PON [3

3. N. Cvijetic, M. Huang, E. Ip, Y. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Proc. OFC/NFOEC2011, paper PDPD7 (2011).

], integration of optical OFDM-PON and wireless communication [4

4. Z. Cao, J. Yu, M. Xia, Q. Tang, Y. Gao, W. Wang, and L. Chen, “Reduction of inter subcarrier interference and frequency-selective fading in OFDM-ROF systems,” J. Lightwave Technol. 28(8), 2423–2429 (2010).

] and architecture of optical OFDM-PON system [5

5. D. Qian, N. Cvijetic, J. Hu, and T. Wang, “A novel OFDMA-PON architecture with source-free ONUs for next-generation optical access networks,” IEEE Photon. Technol. Lett. 21(17), 1265–1267 (2009). [CrossRef]

] have been studied and gained much attention. However, the security in optical OFDM-PON should be also a significant problem, due to the broadcasting nature in the downstream in such a system. Currently, a symmetric key physical layer encryption for wireless OFDM System [6

6. A. Chorti, “Masked-OFDM: a physical layer encryption for future OFDM applications,” in Proc. GLOBECOMW 2011, DOI: 10.1109/GLOCOMW.2010.5700138, 1254–1258 (2011). [CrossRef]

] and security of OFDM-PON using the chaos scrambling [7

7. L. Zhang, X. Xin, B. Liu, and Y. Wang, “Secure OFDM-PON based on chaos scrambling,” IEEE Photon. Technol. Lett. 23(14), 998–1000 (2011). [CrossRef]

] have been studied. However, the physical encryption and the chaos scrambling are still relatively complicated.

2. Operational principle of the proposed scheme

Figure 1
Fig. 1 Principle of the VPN in an optical OFDM-PON, (a) structure of an optical OFDM-PON transmitter; (b) structure of an optical OFDM-PON receiver; (c) subcarrier bands allocation of an optical OFDM-PON.
depicts the principle of the VPN in an optical OFDM-PON. Figure 1(a) shows the structure of an optical OFDM-PON transmitter, the signal processing of an OFDM transmitter consists of serial-to-parallel conversion, symbol mapping, inverse fast Fourier transform (IFFT), cyclic prefix (CP) insertion, digital to analog (D/A) conversion, up-conversion and optical modulation. In the proposed scheme, we divide the OFDM subcarriers into several sub-carrier bands for different kinds of traffics. For example, we can allocate the OLT band for the conventional traffic between each ONU and OLT, the VPN bands for VPN traffic of different VPNs and the different ONU bands for inter-ONU traffic, respectively. The allocation of subcarrier bands is dynamically scheduled by OLT on the demand of ONUs. Figure 1(b) shows the procedure of the OFDM signal receiving. It’s an inverse procedure of the transmitting. After fast Fourier transform (FFT), the spectral distribution of the received signal is the same with the signal before the IFFT in Fig. 1(a). Guard bands are interleaved between every two subcarrier bands in order to separate each band in frequency, as shown in Fig. 1(c).

As we know, one OFDM symbol starting at t = ts can be represented as,
s(t)={i=0N1direct(ttsT/2)exp(j2πfi(tts))fortstts+T0fort<tsort>ts+T,
(1)
where di is the information symbol at the i th subcarrier, N is the number of subcarriers, T is the symbol period, fi = fc + i / T is the frequency of the i th subcarrier (fc is the frequency of the carrier), and rect (t) is the rectangle function, rect(t) = 1 (| t | ≤ T / 2).

One input port of the IFFT corresponds to one subcarrier, and several adjacent ports constitute a subcarrier band. The input ports of the IFFT correspond to the guard bands, which are all set to ‘0’. After the guard bands are added, the input series of the IFFT ports, {di} can be expressed as following,
{di}=d0,d1...dkOLTband,0...0guardband,dk+1,dk+2...d2k+1VPNband,0...0guardband,..........d2k+2...dNmg1ONUband.
(2)
where g, m are the length of the guard band and the number of the guard bands, respectively. After the guard bands are introduced, the information symbol di is only allocated to the subcarriers in the OLT, VPN and ONU band, but not to subcarriers within the guard bands. Each ONU modulates different kinds of data in the corresponding subcarrier bands. For example, the conventional data is allocated to subcarriers 0 to k (d0 to dk) and VPN date is allocated to subcarriers k + 1 to 2k + 1 (dk + 1 to d2k + 1) in Eq. (2). So the VPN traffic, the inter-ONU traffic and the conventional traffic are isolated from each other by interleaving guard bands. The subcarrier bands allocation in an OFDM-PON system is unified. At the OLT, the bands allocation is the same with the ONUs.

Figure 2
Fig. 2 The proposed optical OFDM-PON, (a) network structure of the proposed optical OFDM-PON and corresponding subcarrier band allocation; (b) architecture of the proposed all-optical VPN in an optical OFDM-PON. SMF: single mode fiber, RN: remote node, COF: comb optical filter, Tx: transmitter, Rx: receiver, OF: optical filter, OC: optical coupler, OS: optical splitter, EDFA: erbium-doped fiber amplifier.
depicts the architecture of the proposed all-optical VPN scheme in an optical OFDM-PON. As shown in Fig. 2(a), in the optical OFDM-PON system, there are n ONU groups and each group contains m ONUs. According to the requirements of users, some ONUs in the same ONU group need to establish a VPN communication, which is called intra-VPN communication; some ONUs in different ONU groups need to establish a VPN communication, which is called inter-VPN communication; some ONUs need to establish a non-VPN intercommunication, which is called inter-ONU communication. And the ONUs need the same kind of communication, which compose a group. In our work, we assume there are only one intra-VPN group, one inter-VPN group and one inter-ONU group in the system. So the subcarrier bands are divided into four parts, as shown in the top left corner of Fig. 2(a): an intra-VPN band, an inter-VPN band, an ONU band and an OLT band, for intra-VPN, inter-VPN, inter-ONU and conventional communication, respectively. Figure 2(b) shows the dedicated architecture of the proposed all-optical VPN in optical OFDM-PON. In the uplink, ONUs in the intra-VPN group, inter-VPN group and inter-ONU group utilize the subcarriers of different subcarrier bands allocated above to modulate the corresponding data of different group. And the conventional communication data is modulated by subcarriers in OLT band. The upstream traffics from each ONU combine into one upstream by an optical coupler (OC) at the remote node (RN), and the upstream traffic is then sent to the OLT via the single mode fiber (SMF). At the OLT, the upstream is amplified by an erbium-doped fiber amplifier (EDFA) and split into two parts by an optical splitter (OS). One part directly enters the OLT receiver (Rx) for demodulation. The other part enters an optical filter (OF), which removes the signal in the OLT band and passes the signals in other bands. So the OLT band collision at the OC in the OLT between the upstream traffic and the conventional downstream traffic from the OLT transmitter (Tx) is avoided. The output of the OF is then combined with the traffic from the OLT Tx by an OC. After an EDFA at the OLT, the downstream is transmitted to the RN via the SMF. At the RN, the downstream traffic enters a comb optical filter (COF) bank, which is made up of k COFs. The number of the COF ‘k’ equals the sum of the intra-VPN, the inter-VPN and the inter-ONU groups’ number. The COF bank is used to extract the optical signals in different bands according to the bands allocation. In Fig. 2(b), COF 1 extracts signals in the OLT band and the intra-VPN band and the signals are broadcasted to each ONU in the intra-VPN group by an OS. COF 2 extracts signals in the OLT band and inter-VPN band and the signals are broadcasted to each ONU in the inter-VPN group by an OS. COF k extracts signals in the OLT band and ONU band and the signals are broadcasted to each ONU in the inter-ONU group by an OS. The subcarrier bands, the pass band of OF (in the OLT) and the COF are shown in the lower left corner of Fig. 2(b). In the proposed scheme, only one downstream fiber and one upstream fiber are needed per ONU and only one COF is needed per ONU group. So the system has a good scalability.

3. Simulation setup, results and discussion

In this section, we performed a simulation demonstration to verify the operation principle of the proposed optical OFDM-PON with all-optical VPN and inter-ONU communications, using VPI transmission-Maker Version 8.3. The simulation setup is shown in Fig. 3
Fig. 3 Simulation setup of the proposed optical OFDM-PON, the network architecture, and the corresponding optical spectra of the subcarrier bands. OCh: optical channel, DSP: Digital Signal Processing, BER: Bit error rate. Note that the vertical axis and the horizontal axis of the optical spectra are the optical power (dBm) and the frequency relative to 193.1 THz, respectively.
, whose characterization can be found in Fig. 2. The subcarrier bands allocation (the IFFT input ports allocation) is shown in the top left corner in Fig. 2. The intra-VPN band is for all-optical VPN communication in the same ONU group (ONU 1_1 and ONU 1_3); the inter-VPN band is for all-optical VPN communication between different ONU groups (ONU 1_2 and ONU 2_2); the ONU band is for all-optical inter-ONU communication (ONU 2_1 and ONU 2_3); and the OLT band is for the conventional communication between ONUs and OLT. The optical OFDM-PON architecture and the dedicated optical channels between each ONU and OLT are shown in the middle of Fig. 3. Take the inter-VPN communication between ONU 1_2 and ONU 2_2 for an example: the VPN data of ONU 1_2 is modulated in the inter-VPN band, and the inter-VPN traffic then goes through the dedicated optical channel. In the COF bank, COF 2 is set to extract the inter-VPN band and the OLT band, and it directs the inter-VPN traffic and conventional traffic (from OLT Tx) to ONU 2_2. The other types of communications are fulfilled in the similar way. Additionally, the structure of the transmitter and the receiver of the optical OFDM-PON system can be seen in Fig. 1.

In this work, the IFFT size is 256, corresponding to 256 subcarriers. The subcarriers are divided into four bands: ONU band, inter-VPN band and OLT band containing 50 subcarriers respectively, intra-VPN band containing 49 subcarriers. And each guard band contains 19 subcarriers. This procedure of subcarriers band allocation is done by the Matlab programs. Notably, the subcarrier bands can be allocated unequally on demand and the subcarrier number of the guard band is also tunable. A narrow guard band corresponds to a higher spectral efficiency, which should be wide enough so that the filters can separate each band without damaging signals in other subcarrier bands. The gauss band-pass filters with the bandwidth of 2.2 GHz are used to perform the COF. The generation and the receiving of the optical OFDM signal are shown in the top left corner of Fig. 3. The OFDM baseband signals at 10 Gb/s are generated using the Matlab programs, with 16-QAM symbol mapping and CP of 0.125. The end-to-end OFDM signal bandwidth is 10 GHz. The signal processing of the OFDM base-band signal consists of serial-to-parallel conversion, QAM symbol encoding, IFFT, CP insertion, and DAC. The sampling rate and the resolution of DAC are 4 GS/s and 8 bits, respectively. The base-band OFDM signal is up-converted to 10 GHz RF by analog IQ mixers. The RF OFDM signal drives the MZM with the bandwidth of 10 GHz and the extinction ratio of 25 dB to generate the optical OFDM signal, where the driving voltage on the modulator is set to 4.5 V. The continuous wave (CW) signal with the center frequency of 193.1 THz (1552.52 nm) and the line-width of 10 MHz is generated by a laser with the average power of 0 dBm. An OF with the bandwidth of 20 GHz is used to get the optical single sideband (OSSB) OFDM signal before the optical OFDM signal enters the dedicated optical channel in Fig. 3. The length of the SMF is 25 km. At the receiver side, the optical OFDM signal is detected by a PIN with bandwidth of 20 GHz. The digital signal processing (DSP) is used to demodulate the electronic OFDM signal, and the bit error rate (BER) of the proposed optical OFDM-PON is achieved using the Matlab program.

The sub-graphs (i) to (v) in the right of Fig. 3 show successfully the results of the spectra distribution, which correspond to the subcarrier bands allocation above. Sub-graph (v) corresponds to the combination of (i), (ii), (iii) and (iv). A 10 GHz frequency guard band is created after up-conversion between the central carrier and the OFDM band, as shown in sub-graph (v). After combination, the optical power decreases about 5 dB, however, the optical spectra of different subcarrier bands can be still clearly found from these results.

The BER curves and the corresponding normalized constellations of the intra-VPN, inter-ONU, inter-VPN and OLT traffic (conventional traffic) in the optical OFDM-PON system with back to back and optical fiber transmission, are shown in Figs. 4(a)
Fig. 4 BER curves and normalized constellations of (a) intra-VPN traffic; (b) inter-ONU traffic; (c) inter-VPN traffic; (d) OLT traffic for the proposed optical OFDM-PON.
, 4(b), 4(c) and 4(d), respectively. From these results, we find that the BER performances of different cases can be acceptable. For example, the BER performance reaches about 10−9 at the received optical power of −19.5 dBm for the intra-VPN case with back-to-back; considering the fiber transmission of 25 km, the BER performance deteriorates of about 1 dB, as shown in Fig. 4(a). These results in Fig. 3 and Fig. 4 show that the intra-VPN, inter-ONU, inter-VPN and conventional communications have been realized successfully in the proposed scheme simultaneously.

4. Conclusion

We have proposed and demonstrated a new all-optical VPN scheme operating at 10-Gbit/s with 16 QAM in the optical OFDM-PON. By the subcarrier bands allocation and the establishment of the dedicated optical channels, the all-optical VPN and all-optical inter-ONU communications have been realized. The key advantage of the VPN in the optical OFDM-PON is that the subcarriers can be allocated to different VPN and ONU groups according to the users’ requirements dynamically. So we can make the best use of the system resources and the system has a good scalability. Moreover, the VPN employed in the optical OFDM-PON would enhance the network security.

Acknowledgments

This work is supported by NSFC 61171045, JX0801. The authors would thank anonymous reviewers for the valuable comments that improve the clarity and quality of this paper.

References and links

1.

N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Commun. Mag. 48(7), 70–77 (2010). [CrossRef]

2.

J. L. Wei, C. Sánchez, R. P. Giddings, E. Hugues-Salas, and J. M. Tang, “Significant improvements in optical power budgets of real-time optical OFDM PON systems,” Opt. Express 18(20), 20732–20745 (2010). [CrossRef] [PubMed]

3.

N. Cvijetic, M. Huang, E. Ip, Y. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Proc. OFC/NFOEC2011, paper PDPD7 (2011).

4.

Z. Cao, J. Yu, M. Xia, Q. Tang, Y. Gao, W. Wang, and L. Chen, “Reduction of inter subcarrier interference and frequency-selective fading in OFDM-ROF systems,” J. Lightwave Technol. 28(8), 2423–2429 (2010).

5.

D. Qian, N. Cvijetic, J. Hu, and T. Wang, “A novel OFDMA-PON architecture with source-free ONUs for next-generation optical access networks,” IEEE Photon. Technol. Lett. 21(17), 1265–1267 (2009). [CrossRef]

6.

A. Chorti, “Masked-OFDM: a physical layer encryption for future OFDM applications,” in Proc. GLOBECOMW 2011, DOI: 10.1109/GLOCOMW.2010.5700138, 1254–1258 (2011). [CrossRef]

7.

L. Zhang, X. Xin, B. Liu, and Y. Wang, “Secure OFDM-PON based on chaos scrambling,” IEEE Photon. Technol. Lett. 23(14), 998–1000 (2011). [CrossRef]

8.

Y. Su, P. Hu, W. Hu, J. Zhang, L. Leng, H. He, X. Tian, and Y. Jin, “A packet-switched waveband-selective PON enabling optical internetworking among ONUs,” in Proc. ECOC 2005, 691–692 (2005).

9.

C.-J. Chae, S.-T. Lee, G.-Y. Kim, and H. Park, “A PON system suitable for internetworking optical network units using a fiber Bragg grating on the feeder fiber,” IEEE Photon. Technol. Lett. 11(12), 1686–1688 (1999). [CrossRef]

10.

X. Hu, L. Zhang, P. Cao, G. Zhou, F. Li, and Y. Su, “Reconfigurable and scalable all-optical VPN in WDM PON,” IEEE Photon. Technol. Lett. 23(14), 941–943 (2011). [CrossRef]

11.

Y. Tian, T. Ye, and Y. Su, “Demonstration and scalability analysis of all-optical virtual private network in multiple passive optical networks using ASK/FSK format,” IEEE Photon. Technol. Lett. 19(20), 1595–1597 (2007). [CrossRef]

OCIS Codes
(060.2330) Fiber optics and optical communications : Fiber optics communications
(060.2360) Fiber optics and optical communications : Fiber optics links and subsystems
(060.4230) Fiber optics and optical communications : Multiplexing

ToC Category:
Fiber Optics and Optical Communications

History
Original Manuscript: September 8, 2011
Revised Manuscript: November 9, 2011
Manuscript Accepted: November 11, 2011
Published: November 18, 2011

Citation
Chongfu Zhang, Jian Huang, Chen Chen, and Kun Qiu, "All-optical virtual private network and ONUs communication in optical OFDM-based PON system," Opt. Express 19, 24816-24821 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-24-24816


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. N. Cvijetic, D. Qian, and J. Hu, “100 Gb/s optical access based on optical orthogonal frequency-division multiplexing,” IEEE Commun. Mag.48(7), 70–77 (2010). [CrossRef]
  2. J. L. Wei, C. Sánchez, R. P. Giddings, E. Hugues-Salas, and J. M. Tang, “Significant improvements in optical power budgets of real-time optical OFDM PON systems,” Opt. Express18(20), 20732–20745 (2010). [CrossRef] [PubMed]
  3. N. Cvijetic, M. Huang, E. Ip, Y. Huang, D. Qian, and T. Wang, “1.2 Tb/s symmetric WDM-OFDMA-PON over 90km straight SSMF and 1:32 passive split with digitally-selective ONUs and coherent receiver OLT,” in Proc. OFC/NFOEC2011, paper PDPD7 (2011).
  4. Z. Cao, J. Yu, M. Xia, Q. Tang, Y. Gao, W. Wang, and L. Chen, “Reduction of inter subcarrier interference and frequency-selective fading in OFDM-ROF systems,” J. Lightwave Technol.28(8), 2423–2429 (2010).
  5. D. Qian, N. Cvijetic, J. Hu, and T. Wang, “A novel OFDMA-PON architecture with source-free ONUs for next-generation optical access networks,” IEEE Photon. Technol. Lett.21(17), 1265–1267 (2009). [CrossRef]
  6. A. Chorti, “Masked-OFDM: a physical layer encryption for future OFDM applications,” in Proc. GLOBECOMW 2011, DOI: 10.1109/GLOCOMW.2010.5700138, 1254–1258 (2011). [CrossRef]
  7. L. Zhang, X. Xin, B. Liu, and Y. Wang, “Secure OFDM-PON based on chaos scrambling,” IEEE Photon. Technol. Lett.23(14), 998–1000 (2011). [CrossRef]
  8. Y. Su, P. Hu, W. Hu, J. Zhang, L. Leng, H. He, X. Tian, and Y. Jin, “A packet-switched waveband-selective PON enabling optical internetworking among ONUs,” in Proc. ECOC 2005, 691–692 (2005).
  9. C.-J. Chae, S.-T. Lee, G.-Y. Kim, and H. Park, “A PON system suitable for internetworking optical network units using a fiber Bragg grating on the feeder fiber,” IEEE Photon. Technol. Lett.11(12), 1686–1688 (1999). [CrossRef]
  10. X. Hu, L. Zhang, P. Cao, G. Zhou, F. Li, and Y. Su, “Reconfigurable and scalable all-optical VPN in WDM PON,” IEEE Photon. Technol. Lett.23(14), 941–943 (2011). [CrossRef]
  11. Y. Tian, T. Ye, and Y. Su, “Demonstration and scalability analysis of all-optical virtual private network in multiple passive optical networks using ASK/FSK format,” IEEE Photon. Technol. Lett.19(20), 1595–1597 (2007). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited